Assessment of a newly recognized association. Carotid sinus hypersensitivity and denervation of sternocleidomastoid muscles

Dysautonomia: A Forgotten Condition - Part 1

Dysautonomia covers a range of clinical conditions with different characteristics and prognoses. They are classified as Reflex Syndromes, Postural Orthostatic Tachycardia Syndrome (POTS), Chronic Fatigue Syndrome, Neurogenic Orthostatic Hypotension (nOH) and Carotid Sinus Hypersensitivity Syndrome. Reflex (vasovagal) syndromes will not be discussed in this article. Reflex (vasovagal) syndromes are mostly benign and usually occur in patients without an intrinsic autonomic nervous system (ANS) or heart disease. Therefore, they are usually studied separately. Cardiovascular Autonomic Neuropathy (CAN) is the term most currently used to define dysautonomia with impairment of the sympathetic and/or parasympathetic cardiovascular autonomic nervous system. It can be idiopathic, such as multisystemic atrophy or pure autonomic failure, or secondary to systemic pathologies such as diabetes mellitus, neurodegenerative diseases, Parkinson's disease, dementia syndromes, chronic renal failure, amyloidosis and it may also occur in the elderly. The presence of Cardiovascular Autonomic Neuropathy (CAN) implies greater severity and worse prognosis in various clinical situations. Detection of Orthostatic Hypotension (OH) is a late sign and means greater severity in the context of dysautonomia, defined as Neurogenic Orthostatic Hypotension (nOH). It must be differentiated from hypotension due to hypovolemia or medications, called non-neurogenic orthostatic hypotension (nnOH). OH can result from benign causes, such as acute, chronic hypovolemia or use of various drugs. However, these drugs may only reveal subclinical pictures of Dysautonomia. All drugs of patients with dysautonomic conditions should be reevaluated. Precise diagnosis of CAN and the investigation of the involvement of other organs or systems is extremely important in the clinical suspicion of pandysautonomia. In diabetics, in addition to age and time of disease, other factors are associated with a higher incidence of CAN, such poor glycemic control, hypertension, dyslipidemia and obesity. Among diabetic patients, 38-44% can develop Dysautonomia, with prognostic implications and higher cardiovascular mortality. In the initial stages of DM, autonomic dysfunction involves the parasympathetic system, then the sympathetic system and, later on, it presents as orthostatic hypotension. Valsalva, Respiratory and Orthostatic tests (30:15) are the gold standard methods for the diagnosis of CAN. They can be associated with RR Variability tests in the time domain, and mainly in the frequency domain, to increase the sensitivity (protocol of the 7 tests). These tests can detect initial or subclinical abnormalities and assess severity and prognosis. The Tilt Test should not be the test of choice for investigating CAN at an early stage, as it detects cases at more advanced stages. Tilt response with a dysautonomic pattern (gradual drop in blood pressure without increasing heart rate) may suggest CAN. Treatment of patients at moderate to advanced stages of dysautonomia is quite complex and often refractory, requiring specialized and multidisciplinary evaluation. There is no cure for most types of Dysautonomia at a late stage. NOH patients can progress with supine hypertension in more than 50% of the cases, representing a major therapeutic challenge. The immediate risk and consequences of OH should take precedence over the later risks of supine hypertension and values greater than 160/90 mmHg are tolerable. Sleeping with the head elevated (20-30 cm), not getting up at night, taking short-acting antihypertensive drugs for more severe cases, such as losartan, captopril, clonidine or nitrate patches, may be necessary and effective in some cases. Preventive measures such as postural care; good hydration; higher salt intake; use of compression stockings and abdominal straps; portioned meals; supervised physical activity, mainly sitting, lying down or exercising in the water are important treatment steps. Various drugs can be used for symptomatic nOH, especially fludrocortisone, midodrine and droxidopa, the latter not available in Brazil. The risk of exacerbation or triggering supine hypertension should be considered. Chronic Fatigue Syndrome represents a form of Dysautonomia and has been renamed as a systemic disease of exercise intolerance, with new diagnostic criteria: 1 - Unexplained fatigue, leading to occupational disability for more than 6 months; 2 - Feeling ill after exercising; 3 - Non-restorative sleep; 4 - One of the following findings: cognitive impairment or orthostatic intolerance. Several pathologies today have evolved with chronic fatigue, being called chronic diseases associated with chronic fatigue. Postural orthostatic tachycardia syndrome (POTS), another form of presentation of dysautonomic syndromes, is characterized by sustained elevation of heart rate (HR) ≥30 bpm (≥40 bpm if <20 years) or HR ≥120 bpm, in the first 10 minutes in an orthostatic position or during the tilt test, without classical orthostatic hypotension associated. A slight decrease in blood pressure may occur. Symptoms appear or get worse in an orthostatic position, with dizziness, weakness, pre-syncope, palpitations, and other systemic symptoms being common.

Should We Ever Pace for Carotid Sinus Syndrome?

Carotid sinus syndrome has been associated with transient loss of consciousness for millennia, and while steeped in cardiovascular lore, there is little in the way of solid evidence to guide its main treatment modality, permanent cardiac pacing. This article reviews the history of the condition in the context of its contemporary understanding before examining three key concepts in the consideration of what constitutes a manageable disease: first, is there a pathophysiologic rationale for the disease (in this case carotid sinus syndrome)? Second, is there a good diagnostic test that will identify it reliably? And finally, is there a convincingly evidence-based treatment for the disease? Relevant literature is reviewed, and recommendations made in how we view pacing in the context of this intriguingly opaque condition.

Carotid sinus hypersensitivity: block of the sternocleidomastoid muscle does not affect responses to carotid sinus massage in healthy young adults

The arterial baroreflex is crucial for short‐term blood pressure control – abnormal baroreflex function predisposes to syncope and falling. Hypersensitive responses to carotid baroreflex stimulation using carotid sinus massage (CSM) are common in older adults and may be associated with syncope. The pathophysiology of this hypersensitivity is unknown, but chronic denervation of the sternocleidomastoid muscles is common in elderly patients with carotid sinus hypersensitivity (CSH), and is proposed to interfere with normal integration of afferent firing from the carotid baroreceptors with proprioceptive feedback from the sternocleidomastoids, producing large responses to CSM. We hypothesized that simulation of sternocleidomastoid “denervation” using pharmacological blockade would increase cardiovascular responses to CSM. Thirteen participants received supine and tilted CSM prior to intramuscular injections (6–8 mL distributed over four sites) of 2% lidocaine hydrochloride, and 0.9% saline (placebo) in contralateral sternocleidomastoid muscles. Muscle activation was recorded with electromyography (EMG) during maximal unilateral sternocleidomastoid contraction both pre‐ and postinjection. Supine and tilted CSM were repeated following injections and responses compared to preinjection. Following lidocaine injection, the muscle activation fell to 23 ± 0.04% of the preinjection value (P < 0.001), confirming neural block of the sternocleidomastoid muscles. Cardiac (RRI, RR interval), forearm vascular resistance (FVR), and systolic arterial pressure (SAP) responses to CSM did not increase after lidocaine injection in either supine or tilted positions (supine: ΔRRI −72 ± 31 ms, ΔSAP +2 ± 1 mmHg, ΔFVR +4 ± 4%; tilted: ΔRRI −20 ± 13 ms, ΔSAP +2 ± 2 mmHg, ΔFVR +2 ± 4%; all P > 0.05). Neural block of the sternocleidomastoid muscles does not increase cardiovascular responses to CSM. The pathophysiology of CSH remains unknown.

A case of asystole from carotid sinus hypersensitivity during patient positioning for thyroidectomy

Background

We present a case of a patient with multinodular goiter disease who suffered asystole during head hyperextension for surgical positioning on the operational table.

Case Presentation

Manipulation of carotid sinus may trigger bradycardia or even asystole even in patients without prior history of carotid sinus hypersensitivity. The time proximity between patient positioning and asystole, the late responsiveness to atropine, the immediate increase of heart rate after head elevation and the lack of any other trigger factor or prior history support the hypothesis of carotid sinus syndrome.

Conclusions

Head hyperextension during surgical positioning is not only responsible for jeopardizing blood flow to spinal cord and brainstem but may trigger reflexes, as well, even in patients without prior neck pathology.

Syncope: Case Studies

Syncope, or the sudden loss of consciousness, is a common presenting symptom for evaluation by neurologists. It is not a unique diagnosis but rather a common manifestation of disorders with diverse mechanisms. Loss of consciousness is typically preceded by a prodrome of symptoms and sometimes there is a clear trigger. This article discusses several cases that illustrate the various causes of syncope. Reflex syncope is the most common type and includes neurally mediated, vasovagal, situational, carotid sinus hypersensitivity, and atypical forms. Acute and chronic autonomic neuropathies and neurodegenerative disorders can also present with syncope.

Carotid sinus syndrome

Carotid sinus hypersensitivity, first described less than 65 years ago, is an important and often undiagnosed cause of syncope in the elderly. Its pathophysiology is complex and certain aspects are not completely understood. The timely diagnosis and treatment of this condition can improve morbidity and prevent complications in the elderly. In this article, the prevalence, risk factors, pathophysiology, diagnosis, aspects of carotid sinus massage, and treatment options for the different kinds of carotid sinus hypersensitivity are discussed.

Recurrent episodes of asystole from carotid sinus hypersensitivity triggered by positioning for head and neck surgery

BACKGROUND

We present a case report of a patient with recurrent thyroid carcinoma, previously treated with surgery and radiotherapy, who developed asystolic episodes on 2 occasions as the result of positioning of the neck in hyperextension for head and neck surgery.

METHODS AND RESULTS

In carotid sinus hypersensitivity (CSH), the carotid sinus reflex is greatly exaggerated, resulting in profound bradycardia and asystole. Predisposing risk factors for the development of CSH in this patient included history of previously treated head and neck cancer and the presence of tight surgical scars. His negative cardiovascular history, the time sequence between neck positioning and asystole, and the fact that asystole recurred during the second surgery strongly suggest that CSH was precipitated by hyperextension of the neck during positioning.

CONCLUSIONS

A heightened awareness of this syndrome, close monitoring, and preparedness for timely diagnosis and management are essential for a successful outcome.

Neurally mediated syncope and unexplained or nonaccidental falls in the elderly

Falls and syncope are among the leading causes for which older patients seek hospital admissions. The prevalence of unexplained or nonaccidental falls is high in this group. The clinical spectrum of falls and syncope has been shown to overlap significantly in the elderly. Carotid sinus syndrome and vasovagal syncope, the two common examples of neurally mediated syncope (NMS), have been increasingly recognised as important attributable causes for unexplained falls and syncope. However, in clinical practice NMS is not widely investigated as a cause of fall and is likely to be underdiagnosed.

[Syncope in the elderly: diagnostic utility of carotid sinus massage in the head-up tilt test]

A 71-year-old man presented with a 6-month history of fainting. Consciousness was quickly regained without clouding or confusion. Ancillary investigations were inconclusive and he was treated with carbamazepine. The fainting spells did not cease and he was referred for a tilt-table test exam. In the head-up position (table tilted at 60 degrees), massage of the carotid sinus was immediately followed by asystole, unconsciousness, and a sharp drop in arterial pressure for 5 seconds. The same procedure in the lying position did not elicit clinical symptoms or haemodynamic imbalance. A diagnosis of carotid sinus hypersensitivity with a cardio-inhibitory response pattern was made. Carbamazepine was withdrawn and a double-chamber pacemaker was implanted in his right ventricle. He remained symptom-free for the ensuing 18 months. This case supports the diagnostic utility of carotid sinus massage during the head-up tilt test in patients with unexplained non-convulsive loss of consciousness.

Carotid sinus syndrome

This article reviews the recent literature about carotid sinus syndrome. It looks principally at the various ways in which it may present, the limited knowledge of its pathophysiology, and the role of carotid sinus massage in the investigation of carotid sinus syndrome.

Disorders of Sinus Function

Sinus node dysfunction is a common entity with significant clinical implications. Establishing a diagnosis may, on occasion, tax the skills of the clinician. Many causes have been cited, but no single factor appears to be established. Immunologic abnormalities may play a part in the etiologic process. Clinical invasive electrophysiology studies may be used to establish a diagnosis. In general, medical therapy must be integrated. Controversy exists regarding the best method of permanent pacing. Treatment may need to be individualized to the type of arrhythmia noted. Long-term prognosis is a large factor in choice of therapy, related to the underlying disease. Prevention of atrial fibrillation may occur with dual-chamber pacing; however, anticoagulation appears essential in this patient subgroup. The 5-year mortality rate in these patients is high and does not appear to be significantly improved with artificial pacing. Mortality is prominently influenced by the coexistence of cardiovascular and valvular heart disease. Patients who die do not differ substantially from survivors with regard to type of sinus dysfunction, occurrence of tachyarrhythmia, or distal conduction abnormalities. The survival rate in patients with sick sinus syndrome and congestive heart failure is significantly lower, and the incidence of embolic events remains high in patients with permanent pacing and the sick sinus syndrome. Thus, it has been proposed that all patients exhibiting the bradycardia-tachycardia syndrome be fully anticoagulated. The incidence of atrial fibrillation is significantly lower in patients with atrial demand pacing (22.3% versus 3.9%) than in patients with ventricular pacing and is accompanied by a decreased incidence of systemic embolization (13% versus 1.6%). Reports comparing survival with use of dual-chamber pacing versus ventricular pacing are encouraging in patients with congestive heart failure. At present, the natural history of the disease is unknown; furthermore, clinical risk factors for the development of symptoms have not been defined, and no electrophysiologic measure of sinus node function has been demonstrated to have reliable predictive value. Therefore, common practice has been to withhold pacemaker therapy in the asymptomatic patient.